Technical Field
This disclosure relates to precision metrology, and more particularly to touch probes used in coordinate measurement systems.
Description of the Related Art
Certain coordinate measurement systems, e.g., one-dimensional or three-dimensional measurement systems, such as coordinate measuring machines (CMMs), may obtain measurements of a workpiece using a touch probe configured to detect when a stylus of the touch probe contacts a workpiece. Touch probes use various types of displacement sensors to sense deflection of the touch probe stylus for an indication that it has contacted a workpiece.
An exemplary prior art CMM utilizing a touch probe is described in U.S. Pat. No. 5,526,576 (the '576 patent), which is hereby incorporated herein by reference in its entirety. The '576 patent discloses a movement mechanism comprising multiple drives for moving the touch probe, an associated electronic system including a CANBUS digital communication system or the like, and features related to processing signals in (or from) the touch probe. A mechanical contact touch probe including two-way communication between the probe in a host machine, using only two wires, is described in U.S. Pat. No. 4,817,362 (the '362 patent), which is hereby incorporated herein by reference in its entirety. In the 362 patent, touching a workpiece causes current changes in an electrical circuit within the probe, which is sensed by a current sensing circuit on the host machine. Communication from the machine to the probe is achieved by varying the voltage supplied to the probe, and initiating different functions in the probe based on the sensed supply voltage.
Another exemplary touch probe is disclosed in U.S. Pat. No. 5,755,038 (the '038 patent), which is hereby incorporated herein by reference in its entirety. The '038 patent discloses a compact touch probe that includes three strain gauges that are responsive to the probe's stylus deflection, and an ASIC processor that receives the strain gauge signals and generates an “auto-zeroed” trigger signal that is output to a host machine through a coaxial electrical connector.
While the systems disclosed in the disclosed in the '576, '362, and '038 patents include features related to processing signals in the touch probes, and/or communicating certain types of operating parameters and/or data using a limited number of wires between the touch probe and a host machine, in practice such features have been accompanied by undesirable tradeoffs. Adversely affected factors have included probe size, and/or the number of wires to the touch probe, and/or the related “retrofit ability” for use or compatibility with existing host machine hardware. Other compromised factors include the limited robustness and scope of the signals that are communicated, and/or ease of use, and the like. Improved systems and features which enable touch probes to communicate additional operating data without adding undesirable tradeoffs (e.g., while maintaining a minimum size, ease of use, and retrofit ability) would be desirable.